Electronically controlled hydraulic actuating system

ABSTRACT

An electrically controlled hydraulic actuating system includes a servocontrol including a cylinder, a piston dividing the cylinder into two chambers each provided with a hydraulic connection port, a control valve connected to a hydraulic circuit. A two-way hydraulic pump is driven in rotation by an electric motor driven by power electronics. A switching device allows the connection ports of the chambers to be connected either to the control valve or the pump. The switching device connects the hydraulic connection ports both to the control valve and the pump, so as to allow the servocontrol to be supplied the sum of the hydraulic power delivered by the hydraulic circuit and the hydraulic power generated by the pump actuated by the electric motor.

The present invention relates to an electrically controlled hydraulicactuating system. Although not exclusively, it is particularly suited touse on board aircraft, for controlling parts such as control surfacesfor example.

Electrically controlled hydraulic actuating systems comprising:

a servocontrol, intended to control at least one moving part, such as acontrol surface, and comprising a cylinder inside which a piston towhich said moving part is connected can move, said piston dividing saidcylinder into two chambers, each of which is provided with a hydraulicconnection port, and said servocontrol being provided with a controlvalve, for example of the servovalve or directly controlled valve type,connected to a hydraulic circuit in which a hydraulic fluid underpressure circulates;

a two-way hydraulic pump, driven in rotation by an electric motor drivenby power electronics; and

a switching device allowing said hydraulic connection ports to beconnected either to said control valve or to said pump,

are already known.

In these known systems, actuation of said moving part is, in normaloperation, performed by said servocontrol supplied with hydraulic fluidby said circuit through said valve and said switching device. Bycontrast, in the event of failure of said hydraulic circuit or of saidvalve, the switching device connects said servocontrol to said hydraulicpump. Actuation of said moving part is then, under exceptional operatingcircumstances, the result of the servocontrol being powered by said pumpdriven by the electric motor, through the switching device.

As a result, these systems are generally known by the abbreviation EBHAwhich stands for electrical back-up hydraulic actuator.

Of course, both in normal operation (where the actuating system is beingsupplied from the hydraulic circuit) and in back-up operation (when theactuating system is being supplied from the pump and the electricmotor), such known systems need to be able to provide the maximumperformance needed to actuate said part. The result of this is thereforethat, on the one hand, the hydraulic circuit needs to be designed forthe maximum power of the actuating system and that, on the other hand,although used infrequently, said pump and its accessories need to berobustly engineered, which increases their cost and mass. Furthermore,for the very reason that they are little used, they may be the site ofbreakdowns that are difficult to detect.

The purpose of the present invention is to overcome these drawbacks. Theinvention relates to an electrically controlled hydraulic actuatingsystem of the type recalled hereinabove in which the design not only ofthe pump and its accessories but also of the hydraulic circuit, thevalve and their accessories can be scaled down, while at the same timemaking any breakdowns of the pump and of its accessories more visible.

To this end, according to the invention, the electrically controlledhydraulic actuating system, of the type mentioned hereinabove, isnoteworthy in that said switching device is additionally able to connectsaid hydraulic connection ports of said chambers both to said controlvalve and to said pump, so as to allow said servocontrol to be suppliedthe sum of the hydraulic power delivered by said hydraulic circuit andof the hydraulic power, of electrical origin, generated by said pumpactuated by said electric motor.

Such a system can therefore be termed electrically assisted hydraulicactuator, abbreviated to EAHA.

Thus, by virtue of the present invention, it is possible to providemaximum required performance by summing the hydraulic power and theelectrical power available, the electrical power being used only duringheavy demands for power likely to exceed the hydraulic capability. Inother words, the hydraulic circuit and the control valve (which deliverthe hydraulic power) are engineered to be able to perform mostactuations, which require a power lower than that demanded for maximumperformance. By contrast, the hydraulic pump and its accessories (whichdeliver power of electrical origin) are engineered to supply top-uppower which, when added to said hydraulic power, allows said maximumperformance to be provided. The result of this is that each element ofthe system according to the invention can be engineered according to theactual power (lower than the maximum power of said system) that it hasto provide. In addition, because the “electrical” elements of thesystem, that is to say the motor, the pump and their air accessories,are called upon during operation of said system, their breakdowns cannotremain hidden.

In the system according to the present invention, said switching devicemay consist of a first and a second selectors with specific controls, itbeing possible for said first selector to be inserted between said valveand said connection ports, while the second selector may be arrangedbetween the latter and said pump, and the specific controls of saidfirst and second selectors allowing said hydraulic connection ports tobe connected not only to said control valve or to said pump, but also toboth said control valve and said pump.

As a preference, said first selector:

can adopt either a passing state or a non-passing state;

spontaneously adopts its non-passing state; and

is forced into its passing state by the action of the pressure of thehydraulic fluid of said hydraulic circuit, through a controlled electricvalve.

Furthermore, according to a first embodiment, said second selector:

can adopt either a passing state or a non-passing state;

spontaneously adopts its non-passing state; and

is forced into its passing state by the action of a control device.

As an alternative, said second selector:

can adopt any one of three states, namely a passing state, a non-passingstate or a passive state for which said second selector establishesexternal communication with restriction between said hydraulicconnection ports;

spontaneously adopts said passive state;

is forced into its passing state by the action of a control device; and

is forced into its non-passing state by the action of the pressure ofthe hydraulic fluid of said hydraulic circuit, through said controlledelectric valve.

The figures of the appended drawing will make it easy to understand howthe invention may be achieved. In these figures, identical referencesdenote similar elements.

FIG. 1 schematically illustrates a hydraulic actuating system accordingto the present invention.

FIGS. 2, 3 and 4 respectively illustrate three modes of operation of thesystem of FIG. 1.

FIG. 5 schematically illustrates an alternative form of embodiment ofthe hydraulic actuating system according to the present invention, in apassive mode of operation.

FIGS. 6, 7 and 8 illustrate the system of FIG. 5 in three other modes ofoperation.

The electrically controlled hydraulic actuating system 1 shown in FIG. 1and according to the present invention comprises a servocontrol 2intended to control at least one moving part 3, for example an aircraftcontrol surface. The servocontrol 2 comprises a cylinder 4 inside whicha piston 5 which divides said cylinder 4 into two chambers 6 and 7 canmove. The chambers 6 and 7 are each provided with a hydraulic connectionport 8 and 9, respectively. The piston 5 is secured to a piston rod 10articulated to a wrist pin 11, secured to said moving part 3 in rotationabout an axis 12 (orthogonal to the plane of FIG. 1). It will be readilyunderstood that, when said piston rod 10 moves coaxially to itself inone direction or the other, as indicated by the double-headed arrow 13,the moving part 3 rotates about said axis 12 in the correspondingdirection, as indicated by the double-headed arrow 14.

Each of the connection ports 8 and 9 of the servocontrol 2 can beconnected either to the supply line 15 or to the return line 16 of ahydraulic circuit 17 in which a hydraulic fluid under pressurecirculates, via a control valve 18, for example of the servovalve ordirectly controlled valve type. The control valve 18 is controlled by adevice 19, for example of the solenoid type. Under the action of saidcontrol device 19, the valve 18 can adopt:

a position in which communication between the circuit 17 and theservocontrol 2 is cut (the position depicted in FIG. 1);

a position in which the connection port 8 is connected to the supplyline 15, while the connection port 9 is connected to the return line 16;and

a position for which the connection port 8 is connected to the returnline 16, while the connection port 9 is connected to the supply line 15.

In addition, said connection ports 8 and 9 can be connected respectivelyto the outlets 21 and 22 of a two-way hydraulic pump 23, driven inrotation by an electric motor 24 driven by power electronics 25.

Between the control valve 18 and the connection ports 8 and 9 is mounteda first selector 26, loaded by a spring 27. Said selector 26, under theaction of the spring 27, spontaneously adopts its non-passing positionfor which communication between the control valve 18 and theservocontrol 2 is interrupted.

Likewise, mounted between the pump 23 and the connection ports 8 and 9is a second selector 28, loaded by a spring 29. Said selector 28, underthe action of the spring 29, spontaneously adopts its non-passingposition for which communication between the pump 23 and theservocontrol 2 is interrupted. Furthermore, a control device 30, forexample of the solenoid type, is capable of causing the selector 28 toswitch into its passing position establishing communication between thepump 23 and the servocontrol 2, against the action of the spring 29.

A two-position electric valve 31, controlled by a control device 32against the action of the spring 33, is inserted between the hydrauliccircuit 17 and the selector 26 and is connected to the latter by a line31A. When the control device 32, for example a solenoid, is at rest, thespring 33 presses the electric valve 31 into its position for which saidselector 26 is connected to the return line 16 of the hydraulic circuit17. By contrast, when the control device 32 is active, it compresses thespring 33 and the electric valve 31 is in its passing position for whichthe selector 26 is connected to the supply line 15 of the hydrauliccircuit 17. In the latter position, the pressure of the hydraulic fluidin the line 15 overcomes the action of the spring 27 which means thatthe selector 26 switches into its passing position.

The control devices 19, 30, 32 and the power electronics 25 may becontrolled by a device 34, for example a computer.

The hydraulic actuating system 1 is supplemented by isolation valves 35and 36, mounted respectively on the lines 15 and 16 of the circuit 17,and by a hydraulic accumulator 37 and by resupply valves 38 and 39.

In FIG. 1, the system 1 is depicted in its state of rest, none of thecontrol devices 19, 25, 30 and 32 being activated by the computer 34.

As is illustrated schematically in FIGS. 2, 3 and 4, the system 1 canoperate in three different modes.

In the first mode illustrated in FIG. 2, the computer 34 activates thecontrol device 32 of the electric valve 31, but leaves the controldevice 30 inactive. Under these conditions, the electric valve 31 sendsthe pressure of the line 15 to the selector 26. The result of this isthat said first selector 26 switches into its passing position, saidpressure overcoming the action of the spring 27. As a result, theconnection ports 8 and 9 of the cylinder 2 are isolated from the pump23, whereas they may be placed in communication with the hydraulicnetwork 17, through the control valve 18. As the control device 19 ofthe latter is controlled by the computer 34, the piston 5 and the part 3are therefore actuated simply from the hydraulic fluid of the network17.

In the second mode of operation of the system 1, illustratedschematically in FIG. 3, the computer 34 activates the control device 30of the second selector 28, and the power electronics 25, but leaves thecontrol devices 19 and 32 inactive. As a result, the electric valve 31and the first selector 26 are in their non-passing position and thecontrol valve 18 is inactive. By contrast, the control device 30overcomes the action of the spring 29 and the second selector 28switches into the passing position. As a result, the connection ports 8and 9 of the cylinder 2 are isolated from the hydraulic circuit 17, butare connected to the two-way pump 23 through the second selector 28. Thepiston 5 and the part 3 are then therefore actuated from the pump 23, bydriving of the electric motor 24 by the power electronics 25, themselvescontrolled by the computer 34.

As to the third mode of operation of the system 1, illustrated in FIG.4, this results from joint activation of the control devices 19, 30, 32and of the power electronics 25 by the computer 34. Under theseconditions:

the electric valve 31 and the first selector 26 are passing, as in thefirst mode of operation; and

the second selector 28 is also passing (as in the second mode ofoperation) because the control device 30 has overcome the action of thespring 29.

As a result, the connection ports 8 and 9 of the cylinder 2 areconnected, simultaneously, to the circuit 17, through the control valve18, and to the pump 23. The piston 5 and the part 3 are thereforeactuated jointly from the hydraulic circuit 17 and from the electricallydriven pump 23.

The embodiment 40 of the system of the invention, depicted in FIG. 5, isidentical to the system 1 in FIGS. 1 to 4, except regarding the secondselector. In the case of the system 40, said second selector 41(replacing the second selector 28) comprises, in addition to the passingand non-passing positions, a passive position for which said secondselector 41 establishes external communication with restriction betweenthe hydraulic connection ports 8 and 9 of the cylinder 4. This passiveposition (depicted in FIG. 5) exists when the first selector 26 isnon-passing and is defined by the action of opposing springs 42 and 43.Depending on the level of restriction of the port 44 that makes thiscommunication with restriction, it is possible to obtain a bypassing ofthe cylinder 2, some degree of damping of the movements of the piston 5and of the control surface 3, or alternatively still, almost totalimmobilization of said piston 5.

The passive position of the second selector 41 is in a position that isintermediate between the passing position and the non-passing position.A control device 45 (analogous with the device 30), controlled by thecomputer 34, is capable of causing said second selector 41 to switchfrom its passive position into its passing position. In addition, thesecond selector 41 can switch from its passive position to itsnon-passing position under the action of the pressure of the hydraulicfluid in the supply line 15, through the controlled electric valve 31and a link 31B.

As a result, operation of the system 40 is as follows:

in the first mode, depicted in FIG. 6 and corresponding to FIG. 2, thecontrol device 32 is activated by the computer 34, which leaves thecontrol device 45 unactivated. Under these conditions, the electricvalve 31 sends the pressure of the line 15 to the selectors 26 and 41.The result of this is that said first selector 26 adopts the passingposition and that said second selector 41 switches into the non-passingposition under the action of the pressure of the line 15, aided by thespring 42 and overcoming the action of the spring 43. The controlsurface 3 is then therefore controlled by the hydraulic circuit 17through the control valve 18;

in the second mode, depicted in FIG. 7 and corresponding to FIG. 3, thecomputer 34 activates the control device 45, and the power electronics25, the control device 19 and 32 remaining inactive. As a result, theelectric valve 31 and the first selector 26 are non-passing and thecontrol valve 18 is inactive. By contrast, the control device 45, aidedby the spring 43, overcomes the action of the spring 42. The controlsurface is therefore controlled by the pump 23, itself driven by thecomputer 34 and the power electronics 25;

in the third mode, depicted in FIG. 8 and corresponding to FIG. 4, thecontrol devices 19, 32, 45 and the power electronics 25 are actuatedsimultaneously by the computer 34. The result of this is therefore thatthe electric valve 31 and the first selector 26 are passing and the sameis true of the second selector 41, whose control device 45, aided by thespring 43, overcomes the action of the spring 42 and of the pressure inthe line 31B. As a result, the control surface 3 is actuated jointly bythe hydraulic circuit 17 and by the pump 23.

What is claimed is:
 1. An electrically controlled hydraulic actuatingsystem comprising: a servocontrol, intended to control at least onemoving part and comprising a cylinder inside which a piston to whichsaid moving part is connected can move, said piston dividing saidcylinder into two chambers, each of which is provided with a hydraulicconnection port, and said servocontrol being provided with a controlvalve connected to a hydraulic circuit in which a hydraulic fluid underpressure circulates; a two-way hydraulic pump, driven in rotation by anelectric motor driven by power electronics; and a switching deviceallowing said connection ports of the chambers to be connected either tosaid control valve or to said pump, wherein: said switching device isadditionally able to connect said hydraulic connection ports of thechambers both to said control valve and to said pump, so as to allowsaid servocontrol to be supplied the sum of the hydraulic powerdelivered by said hydraulic circuit and of the hydraulic power, ofelectrical origin, generated by said pump actuated by said electricmotor, and said switching device comprises a first and of a secondselector, with specific controls; said first selector is insertedbetween said control valve and said hydraulic connection ports, whilethe second selector is arranged between the latter and said pump; andthe specific controls of said first and second selectors allow saidhydraulic connection ports to be connected not only to said controlvalve or to said pump, but also to both said control valve and saidpump.
 2. The system as claimed in claim 1, wherein said first selector:can adopt either a passing state or a non-passing state; spontaneouslyadopts its non-passing state; and is forced into its passing state bythe action of the pressure of the hydraulic fluid of said hydrauliccircuit, through a controlled electric valve.
 3. The system as claimedin claim 1, wherein said second selector: can adopt either a passingstate or a non-passing state; spontaneously adopts its non-passingstate; and is forced into its passing state by the action of a controldevice.
 4. The system as claimed in claim 1, wherein said secondselector: can adopt any one of three states, namely a passing state, anon-passing state or alternatively a passive state for which said secondselector establishes external communication with restriction betweensaid hydraulic connection ports; spontaneously adopts said passivestate; is forced into its passing state by the action of a controldevice; and is forced into its non-passing state by the action of thepressure of the hydraulic fluid of said hydraulic circuit, through saidcontrolled electric valve.